The present invention relates to means for locking a gear drive and more particularly, means for locking a gear drive incorporated into a protective roll-type shutter or awning device.
Security type shutters and awnings comprising a plurality of slats made of extruded aluminum, or other material, hingedly interlocked at each edge, and which can be rolled away by winding around a drum or about a rotatable shaft, are generally provided with a gear drive for the drum or rotatable shaft. Such an arrangement is disclosed, for example, in U.S. Pat. No. 4,294,302 assigned to the same assignee as the present application.
Gear drives for the rotatable shaft of a shutter or awning device generally have a driveshaft which is capable of being directly driven in rotation by a hand crank, or by a second shaft in turn hand or power driven through a second gear drive. The gear drive is enclosed in a housing, and the driven shaft and driving shaft are generally coupled by means of a pair of gears having their axes of rotation disposed in planes at right angles to each other. The gears are usually of the bevel type and provide a one-to-one gear ratio, which requires considerable manual effort for cranking heavy shutter assemblies. Moreover, the gear drive is reversible, which requires that some locking means be provided so that the shutter can be maintained in a rolled-up position, or in any intermediate position from completely rolled-up to fully rolled-down.
Means for preventing the reverse rotation of gear drives incorporated in roll-type shutter or awning assemblies are known in the prior art. For example, co-pending application Ser. No. 331,257 filed Dec. 16, 1981, discloses a worm gear drive which, in addition to presenting the advantage of non-reversibility at high gear ratios and resistance to reversibility at lower gear ratios, is provided with a drag brake arrangement for frictionally inhibiting undesired reverse action of the worm gear drive.
It is apparent, however, that mere frictional resistance may be insufficient to withstand the reverse rotational force applied to a driven shaft by a heavy rolled-up awning, especially in low gear-ratio worm gear drives and in bevel and straight gear drives.
In the above-mentioned U.S. Pat. No. 4,294,302, a positive locking mechanism for a gear drive incorporating bevel gears is disclosed which comprises a compression spring urging two sets of mating teeth into engagement with each other. One set of teeth is formed integrally with a portion of the interior of a gear box housing. The other set of teeth is disposed around the periphery of the driveshaft proximate one end. When both sets of mating teeth are engaged, the driving and driven shafts are held against rotation.
In such a configuration, the teeth on the driving shaft and within the gear box housing are disengaged by a driving handle or crank being pressed into a handle socket affixed at the end of the driving shaft projecting from the gear box. The driving handle longitudinally displaces the driving shaft against the pressure of the spring, thereby disengaging the mating teeth on the shaft from the teeth within the housing. Rotation of the unlocked driving shaft by the driving handle can thereafter be performed for raising or lowering the shutter.
Placement of interlocking teeth on the driveshaft and within the gear drive housing is a satisfactory locking means provided that the shutter user remembers to longitudinally displace the driving shaft against the pressure of the compression spring before attempting to rotate the driving shaft with the handle or crank. However, if the user neglects to press the handle into the socket, thereby failing to displace the driving shaft longitudinally, the locking mechanism can be irreparably damaged, which in turn requires replacement of the entire gear drive as the only means for returning the shutter or awning assembly to an operable condition.
What is needed, therefore, is an improved mechanism for locking the gear drive of a shutter or awning device, which can be manufactured at low cost and which is more positive in its braking action than a mere frictional drag brake. Further, a gear drive locking mechanism is needed which is easier to repair than is the replacement of the entire gear drive when a user neglects to disengage the locking means prior to raising or lowering the shutter or awning.